Infrared cameras are currently being used, among other things, to detect slight temperature differences within an object or body being monitored that may be situated at some distance from the infrared sensors or detectors within these cameras. The ability to measure slight temperature differences may be based on the sensitivity of the detectors to the emission of infrared radiation from the body being monitored. In order for an infrared detector to quantify a temperature reading or difference, it is typically calibrated using a source of blackbody radiation, otherwise known as a blackbody.
Apparatus and methods for calibrating infrared detectors are well-known. An infrared blackbody radiates thermal energy in the wavelength ranges of infrared radiation. The ideal blackbody absorbs radiation at all frequencies, and only emits radiation in the target frequency. When calibrating an infrared camera or a similar device that includes an infrared detector, a black body assembly may be positioned at an objective plane (i.e., lens) of the camera. A number of blackbody assemblies available on the market today are effectively a black body positioned within a box having an opening at one end. The lens of the camera to be calibrated may be pointed into this box. However, calibration results can vary based on changes in the positioning of the lens inside the box.
During calibration, infrared flux from the blackbody is permitted to radiate toward the lens through apertures in the blackbody. The magnitude of the infrared flux emitted over unit time by the blackbody is directly proportional to the temperature of a heat emitter within the blackbody assembly. The heat emitter often may be made of a thermally conductive material, such as copper or aluminum, to ensure uniform diffusion of heat across its surface for uniform radiation of infrared photons over its surface area. The larger the heat emitter is in size, the more difficult it is to ensure that each point across the heat emitter is at the same temperature. The temperature of the heat emitter of the blackbody assembly may be regulated by a heating/cooling source, for instance, a thermoelectric cooler (TEC), whose temperature is electronically controlled by a temperature controller, such that the temperature of the heat source can be varied from cooler than the heat emitter to warmer than the heat emitter.
To ensure that the heat emitter is heated or cooled to the correct temperature, a temperature sensing element may be positioned on the surface or inside the heat emitter itself. The output of this sensing element is typically connected back to the temperature controller to complete the temperature regulation loop. The temperature controller will regulate the current sent to the TEC to achieve and maintain the desired temperature level of the heat emitter. A heat sink may be included adjacent the TEC to help remove the heat when the heat emitter has to be cooled below its present temperature. A fan may also be included near the heat sink to speed the process of heat removal when required.
While there are a number of black body assemblies commercially available, these black body assemblies are often bulky and heavy due to the magnitude and range of temperatures that must be reached. For calibration, the camera and the blackbody assembly must be brought together. The relocation of either the camera or the black body assembly may be difficult or even impractical. For example, in an operating room in a hospital where the infrared camera may be mounted to a ceiling suspended arm, it may be inconvenient or even impractical to relocate a bulky black body assembly to the location of the camera for calibration.
Accordingly, it is desirable to provide a black body assembly which can permit quick and easy calibration of the infrared camera without the need to move the camera from its mounted position, allowing the camera to stay in the working position during the calibration.